1. Field of the Invention
This invention relates to an adaptive strategy for adjusting engine control variables.
2. Prior Art
Known methods for selecting spark advance and exhaust recirculation fractions includes the use of engine speed as defines by RPM and engine torque as defined by manifold absolute pressure (MAP). However, the use of these two inputs limits the flexibility with which control characteristics can be selected. It would be desirable to have additional control of engine operating inputs so that engine operation can be better adapted to actual driving conditions.
Conventional engine calibration includes a table of values for spark angle and exhaust gas recirculation (EGR) fraction. For example, in a computer controlled engine, such as that disclosed in U.S. Pat. No. 3,969,614 issued to Moyer et al and assigned to the assignee hereof, the disclosure of which is hereby incorporated by reference, the computer controls the engine by selecting values from these tables based on measurements of instantaneous engine revolutions per minutes (RPM) and manifold absolute pressure (MAP). The tables are developed by a calibration engineer to satisfy the combined requirements of (1) meeting government standard emission requirements, (2) maximizing fuel mileage over city and highway driving, (3) achieving a desirable driveability and (4) minimizing system cost including catalyst size and loading. In making the compromises among feedgas emission levels, mileage, and catalyst size, as indicated by the system inputs of engine RPM and manifold pressure, it is not generally possible to operate the engine at its most efficient calibration. This results in a loss of fuel mileage from the ideal. These are some of the problems this invention overcomes.